"The rover team's assessment is that the bright object is something from the rover, not Martian material. It appears to be a shred of plastic material, likely benign, but it has not been definitively identified."
Our thought: the Martian surface is very old and very untouched. It would be an ideal place to locate artifacts left by alien explorers.
The object is difficult to see in the imagery provided by NASA, but you can pick it out if you enlarge the image in the article. This has been cropped from that image and the contrast slightly altered. The object is the long, pointed bit just to left of center in the frame.